This application is based on application No. 98-30208 filed in the Korean Industrial Property Office on Jul. 27, 1998, the content of which is incorporated hereinto by reference.
a) Field of the Invention
The present invention relates to a method for preparing a cationic surfactant, and more particularly to a method for preparing a new cationic surfactant in which an esterification reaction of a fatty acid and a quaternary reaction of tertiary amine are progressed simultaneously and in a simple method so that an ester group and a hydroxyl group exist in the molecules resulting in excellent biodegradability and solubility in water.
(b) Description of the Related Art
A cationic surfactant, the hydrophilic radical portion of which is dissociated as a cation when dissolved in water, has a structure that is opposite to that of an anionic surfactant (fatty acid soap) such that it is also called an invert soap. A cationic surfactant is not only applied to produce ordinary surface activity effects such as rinsing, emulsification, solubilization, etc., but also displays softening and antistatic effects. A cationic surfactant is classified as a quaternary ammonium compound or an amine derivative depending on its structure.
Although dimethyl dialkyl ammonium chloride (DDAC) has been typically used as a representative cationic surfactant, its consumption has been decreased more and more due to the low biodegradability of DDAC. Therefore, studies related to injecting a group having a biodegradable functional group (such as ester or amide in an alkyl group) into molecules are actively being pursued.
Among the different types of cationic surfactants developed in this manner, quaternary ammonium compound of amidoamine, quaternary ammonium compound of amidoesteramine, imidazoline, and imidazoline ester based cationic surfactants are most commonly used. Examples include an amidoamine compound, and a preparing method and a softener of cationic surfactants using this compound disclosed in Japanese Patent No. Heisei 6-345704; an amidoesteramine compound, and a preparing method and a softener of cationic surfactants using this compound disclosed in Japanese Patent No. Heisei 6-336466; a softener composition containing imidazoline ester disclosed in Japanese Patent No. Heisei 4-257372; and a method for preparing a conditioning compound containing imidazoline disclosed in Japanese Patent No. Heisei 2-1479.
Nevertheless, a wide range of studies to develop cationic surfactants with excellent biodegradability are still being pursued since the biodegradability of the above patents is low despite the improvement over the biodegradability of DDAC. As a result of such research, it has been determined that if an alkyl group, which is a lipophilic part in molecules of a cationic surfactant, includes an easily degradable functional group like an ester group, its biodegradability becomes quite excellent compared with conventional dimethyl dialkyl ammonium chloride, amide based quaternary ammonium compound, and imidazoline based cationic surfactant (Tenside Surfactant Detergent, 1993, 30, 186-191).
Accordingly, various derivatives of quaternary ammonium compound having an ester group in molecules thereof are being widely studied. Typical examples, which have been commercialized, include WO 94-07978 in which a softener and a hair care product were prepared using a cationic surfactant derived from triethanol amine; WO 93/23510 in which a concentrated fabric softener and a biodegradable fabric softener composition were prepared using a cationic surfactant having ester group at two hydrophobic groups; and WO 921/5745 in which a concentrated fabric softener composition was prepared using linear fatty alcohol ethoxylate and polydialkylsiloxane, etc., in imidazoline or imidazoline ester. A concentrated fabric softening and dispersing agent comprising a quaternary ammonium compound prepared from triethanol amine and fatty acid was prepared in WO 94/14935, and a concentrated fabric softener was prepared using a small amount of a quaternary ammonium compound having an ester group in molecules (and a nonionic dispersing agent) in WO 94/13772.
However, in case of the molecules containing the above quaternary ammonium compound with an ester group, solubility in water is so low that the inherent basic properties of the quaternary ammonium compound are deteriorated when large amounts of compounds such as glycerin based, low grade alcohols and nonionic dispersing agents are used in order to maintain the long-term stability of the salt. Further, although the biodegradability of this quaternary ammonium compound has considerably been improved over the existing dimethyl dialkyl ammonium chloride (DDAC), there are still improvements required in this respect.
It is an object of the present invention to provide a method for preparing a cationic surfactant which maintains excellent softening and antistatic properties associated with quaternary ammonium compound characteristics while having a low toxicity, is and highly biodegradable as a result of having a group in its molecules, and also has excellent dispersing properties in water due to its superior solubility in water.
To achieve the above object, the present invention provides a method for preparing a cationic surfactant of the following General Formula 1 prepared by reacting tertiary amine derivatives, epihalohydrin, and fatty acids: 
wherein R1 is a C1-C4 alkyl group; R2 is a C7-C21 linear or branched alkyl or alkenyl group; A is OCOR3, NHCOR3 or OH; R3 is a C7-C21 linear or branched alkyl or alkenyl group; X is a halogen atom; and n is an integral number from 2 to 6.
The present invention will now be described in detail. As will be realized, the invention is capable of modification in various obvious respects, all without departing from the invention. Accordingly, the description is to be regarded as illustrative in nature, and not restrictive.
The present invention is characterized in that a cationic surfactant of the following General Formula 1 is prepared by performing an esterification reaction together with a quaternary reaction without catalysts using reactants of tertiary amine derivatives, fatty acids, and epihalohydrin: 
wherein R1 is a C1-C4 alkyl group; R2 is a C7-C21 linear or branched alkyl or alkenyl group; A is OCOR3, NHCOR3 or OH; R3 is C7-C21 linear or branched alkyl or alkenyl group; X is a halogen atom; and n is an integral number from 2 to 6.
A cationic surfactant of the present invention is readily biodegradable while maintaining the inherent properties of quaternary ammonium compounds, i.e., softness, antistatic properties, etc. at least equal to levels in conventional quaternary ammonium compounds, as well as containing an ester group. Furthermore, it has improved solubilities in water by employing hydrophilic parts in the molecules of the compounds.
The preparing process of this cationic surfactant is represented in the following Reaction Formula 1: 
wherein R1, R2, A , R3, X, and n are the same as in the above General Formula 1.
In the above Reaction Formula, when tertiary amine derivatives, fatty acids, and epihalohydrin are reacted simultaneously, the epihalohydrin and fatty acids are reacted to form an alkyl halide having ester group with the tertiary amine derivative acting as a catalyst. The resulting material is again reacted with tertiary amine derivative resulting in a formation of quaternary ammonium compound.
The above tertiary amine derivative is represented as in the following General Formula 2: 
wherein R1 is a C1-C4 alkyl group; A is OCOR3, NHCOR3 or OH; R3 is a C7-C21 linear or branched alkyl or alkenyl group; and n is an integral number from 2to 6.
The above tertiary amine derivatives are amide or tertiary amine containing ester groups which are synthesized by reacting dialkyl amino alkyl amine or dialkyl hydroxyalkyl amine derivatives with fatty acids. During the synthesis, it is preferable that the reaction temperature is 100 to 200xc2x0 C., the reaction pressure is 1 to 10 atmospheres, and the reaction time is 3 to 20 hours. In case that the tertiary amine containing ester groups are prepared, a catalyst can selectively be used. The usable catalysts are phosphoric acid, hypophosphorous acid, p-toluene sulfonic acid, hydrochloric acid, etc. The consumed amount of the usable catalysts is 0.01 to 1.0 wt % of the total reactant amount.
A mixture of more than one or two fatty acids having a C8-C22 linear or branched alkyl or alkenyl group can be used as the above fatty acid. Examples include octanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, octadecanoic acid, eicosanoic acid, and docosanoic acid. The fatty acids have an equivalent of 0.8 to 1.3 of tertiary amine derivatives. A drawback of the formation of an insufficient amount of the target material occurs when the consumed amount of fatty acid has an equivalent of less than 0.8 in the tertiary amine derivatives. When this equivalent is over 1.3, non-reacted fatty acid and alkyl halide having ester group remain, deteriorating physical properties.
The above epihalohydrin uses an equivalent of 1.0 to 1.3, preferably 1.0 to 1.1, in the tertiary amine derivative. The drawbacks of an increase in toxicity and a deterioration in physical properties occur as a result of the existence of non-reacted tertiary amine when the equivalent of epihalohydrin is less than 1.0 in the tertiary amine. When this equivalent is over 1.3, an insufficient amount of the target material is produced.
In a method for simultaneously reacting the above tertiary amine derivatives, epihalohydrin, and fatty acid, the reaction temperature is between 60 to 120xc2x0 C. and the reaction time is from 5 to 30 hours, and a reaction solvent can be either used or not used. Examples of solvents which can be employed as reaction solvents include water, methanol, ethanol, 1-propanol, 1-butanol, 2-propanol, ethyleneglycol, glycerin, propyleneglycol, polyethyleneglycol, univalent, bivalent, trivalent, polyvalent alcohols, etc. The consumed amount of the reaction solvent is from 10 to 100 wt % of the total reactant amount.